Characterization of CLO7 and its implication in the heterotrimeric G-protein signaling pathway in Arabidopsis

The caleosins are a family of calcium-binding proteins with seven members, CLO1-CLO7, in Arabidopsis thaliana. Many members of the caleosin gene family have been studied in depth, with the exception of CLO7. The structural similarities between the members of this family would suggest they share similar functions. However, the expression patterns of various caleosins across tissue types and in response to abiotic stress, as shown by RNA-seq and ATH1 microarray datasets, implies specific caleosins have specialized functions. Furthermore, some caleosins have been documented as interactors of the heterotrimeric G protein complex in Arabidopsis. The function and expression of CLO7 was therefore explored to determine its role in the heterotrimeric G-protein signaling pathway. The caleosin CLO7 interacts with the Gα subunit of the heterotrimeric G protein complex, GPA1, which was investigated using the bimolecular fluorescence complementation (BiFC) and yeast two-hybrid (Y2H) assays. CLO7 has unique tissue localization in the plant and is found to be expressed in aerial tissues. CLO7 is not induced by abiotic stresses and the tissue localization remains the same. Unlike some of the other caleosins, CLO7 does not play a role in drought tolerance, stomatal closure, or root architecture. CLO7 does affect seed germination in response to ABA treatment and osmotic stress. Genetic analysis indicated that CLO7 and GPA1 act in the same signaling pathway in the regulation of seed germination in response to osmotic stress and ABA hormone treatment